The process innovation is difficult, costly and time-consuming because it mainly depends on limited knowledge and random inspiration of individual. This paper presents a knowledge-based computer aided process innovation (KCAPI) method in order to change this situation. In this method, process knowledge is described with formal format, organized into knowledge chain. The process contradiction matrix (PCM) is used to express the relations between technical conflict items in process problem and corresponding solving theories. At last the technical conflicts can be eliminated iteratively based on PCM via knowledge chain to approach the innovation goal. The KCAPI method can implement the systematic and structured process innovation and improve the innovation efficiency and quality. A welding process innovation instance was shown to confirm this method.